Implantable inductively programmed temperature sensing transponder

ABSTRACT

A method for determining temperature from a transponder utilizing a thermistor and a running counter comprises providing a running count which varies as a function of temperature; latching the count at predetermined time intervals; determining the difference between the values of successive latched counts; aggregating the differences; determining the total elapsed time between a first latched count and a last latched count; dividing the aggregate by the total time to obtain a frequency; and converting the frequency to a temperature based upon the temperature frequency characteristics of the thermistor.

RELATED U.S. PATENT APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 09/502,696, filed on Feb. 11, 2000, which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention is directed to an implantable inductivelyprogrammable temperature sensing transponder, and, more particularly, toa transponder having operations which may be modified through softwarecontrol

Implantable programmable temperature transponders are passive devicesthat are implanted under the skin of laboratory animals, by way ofexample, for positive animal identification. As is known in the art,conventional transponders, such as those sold by Bio Medic Data Systems,Inc. include a coil antenna coupled to an integrated circuit (IC) chip.The chip includes a memory and a thermistor. Circuitry is provided forreceiving an interrogation signal, deriving power from the interrogationsignal, deriving timing clocks from the interrogation signal, andcontrolling the memory and the thermistor to output data stored in thememory or temperature information sensed by the thermistor to theinterrogator. It is also known in the art to program input data to theon-board memory of the transponder.

This prior art transponder has been satisfactory. However, it suffersfrom the disadvantage that the integrated circuitry required too muchpower for operation in the READ MODE. This resulted in the reduced readdistance between the transponder and interrogator. The memory, whichincluded an EEPROM was too small and the temperature data was requiredto be transmitted over the top of sixteen of the memory bits making themunusable. Although the prior art taught locking the data in the memoryto preserve the integrity of the memory, the lock was permanent andcould not be selectively changed by the transponder user as needed.Furthermore, in the prior art, synchronization between the transponderand interrogator has been performed utilizing a preamble of thetransponder's data signal. Because the entire data signal was requiredto be transmitted as well as the preamble during any synchronizationprocess, time was wasted, slowing down the overall programming and/orread cycle. Furthermore, a single temperature reading taken by thetransponder was sent to the interrogator and used as the temperature.Many factors can affect the reading and recording of temperature in atransponder so that there would be fluctuations between successivetemperature readings. In effect, a floating temperature value wouldoccur reducing the precision of the temperature read. Lastly, duringprogramming, utilizing conventional signal encoding techniques, thetiming of the signal transmitted between the transponder andinterrogator was critical. However, because timing was so critical,noise or other environmental factors could readily disrupt the signal,damaging the results.

Accordingly, an implantable programmable temperature transponder whichovercomes the shortcomings of the prior art is desired.

SUMMARY OF THE INVENTION

An implantable programmable temperature transponder includes a receiverfor receiving a programming signal. A memory has a plurality ofaddresses therein. The data being separated into two portions, a datastorage portion and a lock portion, the data portion being capable ofstoring a plurality of subsets of bits, each subset of bitscorresponding to a character. The lock portion stores a plurality oflocks, each lock corresponding to a respective subset of bitscorresponding to each character. An address module addresses eachaddress within the memory. A data module receives data to be programmedand stores data in the memory at the address selected by the addressmodule; the lock section allowing storing of data in the memory at theselected address if the corresponding lock is clear and preventingstoring of data in the memory if the corresponding lock is set.

In a preferred embodiment, the implantable programmable temperaturetransponder includes a comparator for comparing a programming signalwith a reference voltage and outputting a comparison signal in responsethereto. A transmitter receives the comparison signal and outputs afirst indicator signal if the received voltage is less than thereference voltage and outputs a second signal if the input voltage isgreater than the reference voltage; the first signal being the inverseof the second signal for indicating to the interrogator the sufficiencyof the input programming signal. The programming signal may be pulsespace modulated.

In a preferred embodiment, the implantable programmable temperaturetransponder includes a clock generator for enabling current to besupplied to the memory during programming, turning off the current tothe memory after each successive address has been addressed.

A temperature module including a thermistor is coupled to the datamodule. The temperature module includes a free-running counter which iscontinuously counting the output of the thermistor. A clock generatorcounts predetermined periods, the current count of the temperaturemodule counter being latched and output to the interrogator at the endof each period. The interrogator receives a number of these counts, anddetermines the difference between successive counts to obtain aplurality of actual count numbers having occurred in each elapsed timeperiod. These actual counts are then aggregated. The aggregate value ofthe differences is divided by the total time for obtaining the number ofsamples to obtain an average count per time or frequency. Knowing thethermistor's inherent relationship between frequency and temperature,the temperature corresponding to that frequency is known and is outputby the interrogator as the temperature.

Accordingly, it is an object of the invention to provide an improvedimplantable temperature transponder.

Another object of the invention is to provide a transponder whichminimizes power used during programming and reading of the transponder.

A further object of the invention is to provide a transponder whichspeeds up the voltage synchronization process with an interrogator.

Yet another object of the invention is to provide a transponder withexpanded memory and the ability to transmit temperature data separatelyfrom the data stored in memory so that all the memory addresses can beused.

Another object of the invention is to provide a more precise temperaturereading.

Still another object of the invention is to provide a memory whichprovides varying levels of memory protection including the ability forthe transponder user to selectively lock the data stored in the memory.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specifications anddrawings.

The invention, accordingly, comprises the features of constructions,combinations of elements, combinations of steps, and arrangement ofparts which will be exemplified in the construction as hereinafter setforth and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to thefollowing description in connection with the accompanying drawings, inwhich:

FIG. 1 is a block diagram of an interrogator/transponder system;

FIG. 2 is a more detailed block diagram showing the transponder controllogic constructed in accordance with the invention;

FIG. 3 is a schematic diagram showing a format for the memoryconstructed in accordance with the invention;

FIG. 4 is a schematic diagram showing a format for the status byte ofthe memory format constructed in accordance with the invention;

FIG. 5 is a timing diagram of a voltage synchronization indicationsignal sent by the transponder to the interrogator in accordance withthe invention;

FIG. 6 is a timing diagram of a programming signal output in accordancewith the invention;

FIG. 7 is a schematic diagram of a format for the content of theprogramming signal;

FIGS. 8(A), 8(B) are flow charts showing the method for programming thetransponder in accordance with the invention;

FIGS. 9(A), 9(B) are flow charts showing the method for measuring thetemperature in accordance with the invention;

FIG. 10 is a flow chart showing the method for determining the integrityof the data read from the transponder; and

FIG. 11 is a circuit diagram of a clamp circuit constructed inaccordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is first made to FIG. 1 in which an interrogator, generallyindicated as 10 and a transponder generally indicated as 20 are shown.Interrogator 10 and transponder 20 communicate with each other throughinductive coupling as known in the art from U.S. Pat. No. 4,730,188. Aswill be discussed below, interrogator 10 provides a signal totransponder 20 which provides power to transponder 20, a clock signaland an operational command such as enter the PROGRAM MODE or TEMPERATUREMODE. Transponder 20 sends a return signal containing informationtherein to interrogator 10 as is known in the art.

Interrogator 10 includes a CPU 12 for generating command/power/clocksignals (collectively interrogator signals) in response to the userinputs. These signals are input to an antenna 14 for broadcast totransponder 20.

An antenna 22 within transponder 20 receives the interrogator signalfrom interrogator 10 and inputs a 364 kHz signal to a rectifier 24 (FIG.2) which receives the AC signal from the antenna 22 and rectifies thesignal. The rectified signal is then passed to a control logic circuit26 which, in response to the rectified interrogator signal will eitherread out data from the memory 28, program data into a memory 28, or readout temperature data from a temperature module 30. Temperature module 30includes a thermistor 32 which changes resistance levels in response tochanges in temperature which can be converted into a frequency as isknown in the art, the frequency changing as a function of temperature.The temperature data and data from memory 28 are output under thecontrol of control logic 26 through a modulator 34 for modulating thesignal as known in the art to be transmitted by antenna 22 back tointerrogator 10 where the data is operated upon by CPU 12 ofinterrogator 10.

Reference is now made to FIG. 2 in which a block diagram showing thecircuitry of transponder 20, and in particular control logic 26, ingreater detail is provided. The rectifier 24 includes a diodearrangement for rectifying the input signal and a clamp 23 forregulating the voltage level Vss to the transponder components of the.Clamp 23 simulates the behavior of a Zener diode. Clamp 23 includes fourmetal oxide semiconductor field effect transistors (MOSFETs) Q1-Q4,resistors R1-R3, and voltage connections Vpos and Vss. In effect, theelectronic circuit is a MOSFET Zener circuit providing IC protection tothe remainder of the transponder circuitry by clamping the voltage. TheMOSFET Zener clamp 23 connects Vpos to the incoming positive voltagepower supply and connects Vss to ground.

In clamp 23, transistors Q1 and Q4 are N-channel MOSFETs, whiletransistors Q2 and Q3 are P-channel MOSFETs. Transistor Q4 must be muchlarger in size than transistors Q1-Q3 because it must be able to pass alarge amount of current from Vpos to Vss. In a preferred embodiment,transistor Q4 is at least twenty times larger than the other MOSFETs.

As shown in FIG. 11, resistor R1 is connected at one end to Vpos and atthe other end it is connected to the gate of transistor Q1 and toresistor R2. Resistor R2 is connected at one end to the gate oftransistor Q1 and resistor R1 and at its other end is connected to Vss.Resistor R3 is connected at one end to the gate of transistor Q4 and thedrain of transistor Q3 and the other end is connected to Vss. The gateof transistor Q1 is connected to resistors R1, R2 while the source oftransistor Q1 is connected to Vss and the drain is connected to thegates of transistors Q2, Q3 and the drain of transistor Q2. The gate oftransistor Q2 is connected to the gate of transistor Q3, the drain oftransistor Q1 and its own drain. The source of transistor Q2 isconnected to Vpos and the drain of transistor Q2 is connected to thedrain of transistor Q1 and the gates of transistors Q2, Q3. The drain oftransistor Q3 is connected to resistor R3 and the gate of transistor Q4.The drain of transistor Q4 is connected to Vpos.

During operation, resistors R1, R2 act as a voltage divider and controlclamp threshold voltage. When the voltage on the gate of transistor Q1rises, transistor Q1 will turn on, allowing current to pass through itsdrain and source. Transistors Q2, Q3 act as a current mirror so thatwhatever current is on the drain of transistor Q2 is the same amount ofcurrent on the drain of transistor Q3. With a current on the source oftransistor Q3 and resistor R3, a voltage will be present on the gate oftransistor Q4. The value of transistor. The value of transistor R3determines the gain of the device. In other words, with a large valuefor resistor R3, the voltage on the gate of transistor Q4 rises fasterthan the voltages at Vpos. The value of transistor R3 then controls thespeed at which the clamp acts.

As the voltage rises on the gate of transistor Q4, it will turn on,allowing current to pass through the drain and source. When transistorQ4 dumps current from Vpos to Vss, this keeps the voltage of Vpos at aconstant level thereby clamping the supply voltage to the remainder ofthe integrated circuit, protecting the integrated circuit from adamaging over voltage condition. In a preferred embodiment transistor Q1will start to turn on at approximately four volts and transistor Q4 willturn on and dump enough current to limit Vpos to approximately fivevolts.

Clamp 23 limits the supply voltage for the rest of the integratedcircuit. Usually, integrated circuit devices do not need voltagelimitation as integrated circuit devices are used with a controlledpower source. In other words, the range of voltage that must be suppliedto the chip and any regulation or limitation of power is done off chip.On the other hand, because the transponder is powered by an interrogatorwhich provides an unknown voltage level to the interrogator, theprotection from an over voltage condition is supplied on chip by theclamp.

The rectified signal serves as a master clock input to a clock generator36. Clock generator 36 divides down the master clock signal and providestiming signals and enabling signals to a data module 40, address module38, and memory 28.

Control logic 26 includes address module 38 for receiving signals fromthe clock generator and addressing an identified address within memory28 in response to the clock generator signals. A data module 40 receiveslatch signals from clock generator 36, data from memory 28, temperaturedata from temperature module 30 and outputs data in response to thesesignals to a transmitter 42. Transmitter 42 transmits an output signalcontaining the data through modulator 34 which modulates the outputsignal output by transmitter 42.

A receiver 44 receives the data signal output by interrogator 10 afterprocessing by a comparator 47 and outputs the received data to addressmodule 38. A program control 46 receives data from memory 28 and aprogram bit from data module 40, an address from address module 38 andin response thereto outputs a program enable signal to clock generator36 which in turn enables the programming of data in memory 28.

As described below, comparator 47 also acts as a voltage synchronizationcircuit and receives the interrogator signal and compares theinterrogator signal to a reference voltage; 2.5 volts by way of example.The comparator outputs a signal in response to the received interrogatorsignal and outputs the signal to the transmitter 42 which, in turn,outputs the signal through modulator 34 to antenna 22 to be transmittedto interrogator 10.

As shown in FIG. 3, in a preferred embodiment, memory 28 is an EEPROM.Memory 28 is structured so as to have a status byte region 50, atemperature calibration region 52, a CRC region 54, a data region 56,and a user lock region 58. Temperature calibration region 52 includes atemperature adjustment value which is the offset between the calculatedor sensed temperature sensed by temperature module 30 and the actualtemperature of whatever is being monitored. The data stored intemperature calibration portion 52 is output to interrogator 10 alongwith temperature data from temperature module 30 and interrogator 10through CPU 12 calculates the actual temperature as is known in the art.

CRC region 54 is an integrity check for the data stored in memory 28 asis known in the art, utilizing standard polynomial equations to compareand verify the data in memory.

Data region 56 stores user programmable information input frominterrogator 10 while in PROGRAM MODE as discussed below and read fromthe memory during READ MODE. The data is stored as bits 57 which incombination represent characters. In a preferred embodiment, the leastsignificant character is stored with the least significant bit of thecharacter starting at the least significant bit in the least significantbyte of data region 56 and goes upwards to the most significant bit ofthe character and the most significant bit in the most significant byteof data region 56. A number of bits 57 corresponds to a character. In apreferred embodiment, utilizing the compression techniques, eachcharacter can be represented by less than one byte. In a preferredembodiment, the data portion stores enough data to represent 32characters formed as a plurality of discrete subsets of bits 57 in dataregion 56.

User lock region 58 is divided into bits 59. Each bit corresponds to acharacter stored in data region 56. Each bit represents the lock stateof the respective character in the data. For example, if a zero isstored in the least significant bit of the user lock region whichcorresponds to the bits corresponding to the least significant bits forthe least significant character stored in data region 56 then the lockis “clear”. The user lock bit is “set” by storing a one in the desiredbit of user lock region 58. For example, if the character data is storedas bytes, the least significant bit of the least significant byte ofuser lock region 58 corresponds to the least significant character indata region 56 and the most significant bit of the most significant bytecorresponds to the most significant character. It should be noted thatany other mapping arrangement of lock bits to character bits may beused.

As shown in FIG. 4, status byte 50 includes information for controllingthe operation on memory 28. Status byte 50 includes a mode bit 76 whichcauses the transponder to operate on all of its internal memory or justa portion thereof. This bit directly provides an output to the programcontrol 46 and, in effect, is “hard wired” to automatically control thetransponder circuitry. Specifically, as discussed in detail below, ifmode bit 76 is clear, i.e., contains a zero therein, then thetransponder will transmit or read from all of memory 28. If mode bit 76is a one, then transponder 20 may only read from or program into aportion of memory 28 such as the first half of memory 28.

Bits 68 through 74 collectively indicate to the interrogator andtransponder the type of transponder that transponder 20 is. For example,if there is an extended memory within transponder 20, then a one may bestored in bit 74 to indicate that transponder 20 is an extended memorytransponder (EMT). Bits 68, 70, and 72 may further identify thetransponder type such as a laboratory transponder or industrial usetransponder to determine a transponder data format most suitable for itsintended purpose. Bits 68 through 74 are not hard wired, and thereforeare not automatically input to program control 46. Bits 68-74 may alsobe addressed and reprogrammed by address module 38 and data module 40 toconform transponder 20 to the user's needs.

An HLOCK bit 66 causes program control 46 to disable clock generator 36in the PROGRAM MODE if the HLOCK bit is set (i.e., has a value of one).If the HLOCK is clear, i.e., has a value of zero, then programming canoccur. By disabling the clock generator 36, no data can be written tothe address module 38 and data module 40 into memory 28. This bit 66 ishard wired to program control 46 and controls programming of all of thecharacters in temperature calibration region 52, CRC region 54, dataregion 56, and user lock region 58 not selective characters in dataregion 56 like user lock 58. The HLOCK bit can be addressed andreprogrammed utilizing address module 38 and data module 40 as discussedbelow, and is used to prevent accidental or inadvertent overwriting ofthe data in memory 28.

SEAL lock bits 62, 64 hold two bits in combination which can act to sealtransponder 20 from any future re-write, making the transponder apermanently read-only transponder. Bits 62, 64 are also hard wired toprogram control 46 and cause clock generator 36 to be disabled in thePROGRAM MODE. However, unlike the HLOCK bit 66, SEAL bits 62, 64 are notreprogrammable once they are set. To seal the transponder, SEAL 0 shouldbe set during a first write command and on a second write process SEAL 1should then be set.

It should be noted that the format described above from leastsignificant bit to most significant bit and the relative placement ofthe different memory regions is by way of example. The individual bitscan be arranged in any order as long as one group of bits stores data,one group of bits is mapped to the data bits to act as a lock, and onegroup of bits acts to prevent programming of the data region as a whole.

The clamp 23 is entirely built, utilizing a CMOS Process, into theintegrated circuit devices. Normally, integrated circuit devices such asclamp 23 are built using a bipolar process. A mixed process ofbipolar/CMOS is not feasible in making the integrated circuit yet aZener Diode is still needed in the integrated circuit so that the MOSFETZener Diode formed from the CMOS process is used instead.

Mode

When a continuous voltage signal is received from interrogator 10, clockgenerator 36 utilizes the interrogator signal as a master clock andoutputs a READ EEPROM signal to memory 28 and an INCR ADDR signal toaddress module 38 which causes address module 38 to sequentially latchthe addresses of the memory 28 along the address bus. This causes theaddressed data to be output along a DATA BUS to data module 40 where itis then output as a DATA OUT signal to transmitter 42. Transmitter 42then outputs the data to modulator 32 which outputs a modulated signalto interrogator 10 through antenna 22. Clock generator 36 continuouslyprovides a clock to address module 38 to increment the address beinglatched by address module 38 while in the READ MODE.

During the READ MODE, clock generator 36 provides a READ EEPROM signalto memory 28. As READ EEPROM signal is input to memory 28, memory 28 isutilizing current. However, during operation of a preferred embodiment,the READ EEPROM signal is output to memory 28 only while address module38 latches the address in memory 28 and data is output to data module40. Once the data is output along the DATA BUS, the READ EEPROM signalis disabled until clock generator 36 outputs a successive INCR ADDRsignal to increase the address to be addressed by the address module 38.The READ EEPROM signal is then enabled and current is supplied to memory28 to allow reading of data in memory 28 and this process is repeateduntil the READ MODE is terminated when power is removed from transponder20. By cutting off the current supply to memory 28, the overall currentconsumed during the READ MODE is lowered. Because the memory is inEEPROM, i.e., a static memory, the data is stored even in the absence ofcurrent being supplied to memory 28.

Clock generator 36 outputs a PREAMBLE ENABLE signal to transmitter 42causing transmitter 42 to output a preamble as is known in the art.After a predetermined time period sufficient to output the preamble,clock generator disables the preamble and outputs a DATA ENABLE signalto transmitter 42 causing transmitter 42 to output the DATA OUT signalcontaining the data from data module 40 so that during the READ MODE,the output of transponder 20 is a preamble followed by the data readfrom memory 28 which has been modulated by modulator 34. Once a completecycle of the DATA OUT signal has been output by transmitter 42, clockgenerator 36 disables the DATA ENABLE and outputs the PREAMBLE ENABLEsignal.

Program Mode

Reference is now also made to FIGS. 6-8 in which the operation of thePROGRAM MODE is illustrated. In order to begin programming, transponder20 is first read in the READ MODE and the data is verified using data inCRC region 54 of memory 28 in a step 100. Transponder 20 then transmitsthe data stored in memory 28 as discussed above. Interrogator 10 willthen power down antenna 14, in effect turning off transponder 20.Interrogator 10 will then formulate the data to be written into memory28, i.e. programmed into status byte 50, temperature calibration region52, CRC region 54, data region 56 or user lock region 58 in a step 102.Interrogator 10 formulates a data string corresponding to each bit ofmemory 28, even if that bit is not to be reprogrammed. Interrogator 10utilizing CPU 12 will then analyze the data stored in memory 28. Theinterrogator will analyze status byte 50 to determine whether or notbits 62, 64 of status byte 50 are set in a step 104. If status bytes 62,64 are set, then programming is canceled by the interrogator in a step106.

In a step 108 it is determined whether any bits 57 in data region 56 tobe overwritten (reprogrammed) has a corresponding bit 59 in user lockregion 58 which is set. If so, then this indicates that the character isnot to be changed unless the user lock bit 59 is cleared so writing iscanceled in step 106. A separate programming signal must then be sent toclear the user lock.

If the user lock bit 59 corresponding to a character to be reprogrammedis not set then a transponder programming pass for processing all memorylocations in memory 28 is performed in a step 112.

Reference is now made to FIG. 8(B). The Nth byte (or subset of bits) ofdata (corresponding to a character) stored in data region 56 is comparedwith the Nth byte of the write data in a step 114. If the bytes are thesame as determined in a step 116, there is no need to reprogram memory28 at that data region address and it is determined whether any morebytes are required to be compared in a step 124.

If the bytes are different as determined in step 116 then in a step 118it is determined whether the voltage has been synchronized and if not,voltage synchronization is performed in a step 120. The interrogator andthe transponder must first confirm that there is sufficient voltagelevel for the interrogator signal as received at the transponder for thetransponder to properly operate. In an exemplary embodiment, thisvoltage level is determined to be 2.5 volts. In other words, the signalfrom the interrogator must produce at least 2.5 volts at the transponderin order to effectively transmit data to the transponder and the 2.5volt threshold may be used to determine the difference between a zerosignal value and a one signal value.

In order to transmit data to the transponder 20, interrogator 10 mustdetermine what output power level will produce the reference voltage atthe transponder. This relationship will change as the distance betweenthe interrogator 10 and transponder 20 changes. Transponder 20 assistsinterrogator 10 in determining this power level by sending feedback inthe form of transmitted data that the interrogator 10 can read. Thefeedback tells interrogator 10 whether the voltage at transponder 20 ispresently above or below the threshold voltage.

In step 120 interrogator 10 sends a signal which powers up transponder20. The interrogator signal is received at antenna 22 and input tocomparator 47 where the interrogator signal is compared with a referencevoltage REF. By way of example, if the interrogator signal is greaterthan the reference voltage, comparator 47 outputs a high signal.Conversely, if the received signal is less than the reference voltage,comparator 47 will output a low signal. Comparator 47 outputs an ENCODEDRCV DATA signal which is input to transmitter 42. In a preferredembodiment, transmitter 42 will output a first signal a as shown in FIG.5 if the transponder voltage is below the reference voltage and a secondsignal b shown in FIG. 5 if the transponder voltage is above 2.5 volts.

If the pattern received by interrogator 10 indicates that the inputvoltage is above the desired threshold, i.e., signal b, interrogator 10reduces the power output and the process is repeated until a patternindicating below the threshold is received by the interrogator. Oncesignal a, which is the inverse of signal b, is output, indicating tointerrogator 10 that the voltage received is below the threshold voltageafter an adjustment, the power output by interrogator 10 would beincreased. This process is repeated until the adjustment required fromthe interrogator is too fine, i.e., beyond the capabilities of theinterrogator to further adjust above or below the threshold voltage. Inan alternative embodiment, once an adjustment has become too fine,transponder 20 outputs a signal to interrogator 10 to discontinueadjustment.

By changing the output power level and monitoring the feedback signal,interrogator 10 can deduce the output power level that produces thethreshold voltage (2.5 volts) at transponder 20. Once this thresholdlevel is determined, interrogator 10 is able to transmit data totransponder 20 because it knows how to produce an output power that willresult in a voltage greater than 2.5 volts at the transponder andconversely it knows the output power that will produce less than 2.5volts at transponder 20. Transponder 20 translates a voltage of lessthan a threshold voltage as a zero logic state and a voltage greaterthan the threshold voltage as a one logic state. Transponder 20 powersup in the feedback mode so that interrogator 10 can quickly determinethe threshold voltage transition level. If, however, interrogator 10 isnot interested in programming the transponder, it can simply set aconstant output power level and wait until transponder 20 switches tothe READ MODE and read data from transponder 20.

Once the voltage has been synchronized in step 120 it is determinedwhether HLOCK bit 66 has been set in step 121. If so, then HLOCK bit 66must be cleared to permit programming in a step 123. In step 123 aprogram signal is sent by interrogator 10 to clear HLOCK bit 66.

The program signal has a data format as shown in FIG. 7 in which programsignal 200 has a program region 202, a data region 204, and an addressregion 206. The program region 202 is a single bit, in a preferredembodiment, indicating that the signal is, in fact, a program signal.The data region 204 includes the data to be programmed into memory 28and represents a single character. In a preferred embodiment eachcharacter is one byte in length and data region 204 is made up of 8bits, and with compression techniques each character can be representedby less than eight bits, while the data region can remain 8 bits long toprogram two bits for example if compressed to six bits, of a successivecharacter. Address region 206 contains the data for indicating theaddress at which the data of the data region 204 is to be written and ina preferred embodiment is five bits.

As shown in FIG. 6, the actual signal transmitted by interrogator 10which embodies the data of data signal 200 is pulse space modulated.FIG. 6 is a timing diagram of an exemplary signal. In prior artinductively coupled transponders, the communication between theinterrogator and the transponder was heavily dependent upon the timingof the transmit and receive signals between the two. The signal in thepresent invention is timing independent. The signal is made up of aseries of fixed or standard pulses 210, the width or spacing betweenthese pulses is modulated by a delay to correspond to the desired data.For example, a zero may correspond to a standard spacing between twopulses 210 while a data 1 is represented by a delayed or elongatedspacing between adjacent pulses 210. As a result, timing is no longer afactor. The end of a data transmission cycle may be indicated byremaining in a logic level for a predetermined period of timecorresponding to more than the standard pulse or the value of a logiczero or logic one. This is how programming starts in a step 122.

Receiver 44 receives the data as well as a transmit clock from clockgenerator 36. If receiver 44 detects the leading edge transition of apulse 210, it then begins comparing the space between the pulses with acount dependent upon the XMIT CLK signal from clock generator 36, forexample, eight cycles of the transmit clock. If the received pulse widthis less than the transmit clock, then, by way of example, the receiverwill determine that the derived data is a zero and transmit that zero tothe address module 38 as the RCV DATA signal along with a RCV CLK signalfor clocking the data into the address module 38. On the other hand, ifthe length of the width of the space is longer than the counted cyclesof the transmit clock, it determines that the received data is a one andwill transmit a one to address module 38 along with a RCV CLK signal forclocking the data into address module 38. If the detected pulse has awidth greater than a predetermined number of cycles, then receiver 44determines that the data transmission has been completed and a XMITCOMPLETE signal is input to address module 38. As the data is shiftedinto address module 38, it is then shifted as RCV DATA SEQUENCE signalto data module 40 so that the first 8 bits, by way of example,corresponding to data portion 204 of the data signal are latched in datamodule 40. Additionally, the program bit of program region 202 is outputto program control 46 to indicate programming is to occur.

If interrogator 10 does not have a CPU 12 with the software capabilityfor determining that the data has been locked by a comparison of theread data stream, programming will still be prevented by an interrogatorbecause of program control 46. When all of the data has been received byreceiver 44, the program bit has been received by program control 46,program control 46 looks at the status byte 50 of memory 28 anddetermines whether or not the seal bits 62, 64 of status byte 50 havebeen set. If seal bits 62, 64 have been activated, program control 46will not output a PROGRAM ENABLE signal to clock generator 36. Clockgenerator 36 will not clock the address module 38 or data module 40.Therefore, the programming cannot be forced by the interrogator.

If either one of seal bits 62, 64 are clear in this embodiment, programcontrol 46 then looks to HLOCK bit 66 which is also hard wired intoprogram control 46. If HLOCK bit 66 has been set then again the programcontrol 46 will not output the PROGRAM ENABLE signal to beginprogramming as determined in a step 121.

Because HLOCK bit 66 is reprogrammable, in step 123 program control 46determines whether or not the address indicated by address module 38along the address bus corresponds to the status byte 50 of memory 28. Ifthe address indicated by address module 38 is the status byte, programcontrol 46 outputs a PROGRAM ENABLE signal to clock generator 36. If theaddress is not the status byte, then it will not enable clock generator36 preventing programming of any of the temperature calibration region52, CRC region 54, remaining bits of the data region 56 or user lockregion 58.

In step 123, interrogator 10 outputs program signal 200 containing theaddress of status byte 50 in address region 206 and a zero for bit 66 indata region 204. Because the address of the programmed byte is thestatus byte, program control 46 outputs a PROGRAM ENABLE signal to clockgenerator 36. Clock generator 36 clocks the address module along theADDR LATCH input to clock the status byte address causing it to send asignal of the specific address of memory 28 and also outputs a LATCHDATA signal to data module 40 which causes data module 40 to shift data204 of data signal 200 into memory 28 at the address indicated byaddress module 38. This, in effect, will unlock the HLOCK bit 66 byplacing a zero in HLOCK bit 66.

Once HLOCK bit 66 has been cleared in step 123, or if it was determinedthat HLOCK bit 66 was clear in step 121, in a step 122 the Nth byte ofwrite data is programmed into the transponder in a manner identical toprogramming the HLOCK. Program control 46, after confirming that theHLOCK bit 66 is clear, outputs a PROGRAM ENABLE signal which causesclock generator 36 to clock address module 38 to address the desiredmemory address as indicated by the data stored in address region 206 ofdata signal 200. The data of data region 204 latched into data module 40is input to memory 28 at the indicated address. It is then determined ina step 124 whether there are any more bytes to compare in a step 114.

If there are no more bytes to compare, then for safe keeping, althoughoptional, the HLOCK bit 66 is programmed to be set by first determiningif the bit is clear in a step 126. If the bit is clear it is programmedto be set in step 128. Again, programming is the same as that in step123 only the value of the data being changed in bit 66 is different. Ina step 130 it is determined whether any bytes are programmed.

If bytes from memory 28 have been programmed, then the transponder isagain read in step 110 and the data read from the transponder iscompared with the data that was to be programmed by the interrogator 10under the control of CPU 12. If any bytes are different, thentransponder 20 would be reprogrammed to correct those differences in astep 112. If there are no differences between the bytes of data storedas compared to the bytes of data intended to be programmed, thenprogramming is finished in a step 132, which would be arrived at bydetermining that in a second go around, no bytes were again programmedin step 130.

If, in step 108 it is determined that one or more user lock bits 59corresponding to a character is set, a separate programming signal mustbe sent to clear the user lock. User lock region 58 is programmed toclear the desired bits. This programming is done in a manner similar tothat for programming the HLOCK bit including resetting user lock bit 59after programming the corresponding character bits 57 if desired.

During programming, clock generator 36 outputs a PROGRAM EEPROM signalto memory 28. This signal enables current to memory 28 to allow it to beoperated on. Clock generator 36 counts from the time PROGRAM ENABLEenables the clock generator 36 and for a predetermined period sufficientto shift data from data module 40 into the EEPROM of memory 28. Once thepredetermined count has been reached, PROGRAM EEPROM is disabled so thatno current is provided to the memory, further conserving power.

Program control 46 also reads mode bit 76 of status byte 50. If mode bit76 is set for example, only half or 16 characters of data region 56 canbe accessed either for programming or reading. Mode bit 76 causesprogram control 46 to output a MODE signal to address module 38 whichdisables address module 38 from addressing or latching data in thesecond half of memory 28. As a result, the transponder will act as if ithas a memory half the size. This is beneficial where a study utilizingsmaller transponders can be mimicked so that a single transponder canmimic the style of an old study or a new study utilizing theprogrammable implantable transponder of the invention.

Lastly, if the data in data region 56 is to be permanently maintained,then seal bits 62, 64 may be set by programming ones into them. This isaccomplished by first programming SEAL 0, then programming SEAL 1 in away as described above with programming the HLOCK bit. In this way aprogrammable lock bit is provided. It should be noted that two bits areused as the permanent seal by way of example, but the seal bit could beone bit, two bits, three bits or more.

Temperature Mode

During the TEMPERATURE MODE, the transponder is first read in a step 300as shown in FIGS. 9(A), 9(B). In a step 302, voltage synchronization isperformed to make sure that an appropriate voltage level temperaturecommand will be sent and received. The voltage synchronization is thatdescribed above utilizing comparator 47. A temperature command is sentby interrogator 10 in a step 304 as a pulse space modulated signal asshown in FIG. 6. The signal may be of any length, but in the preferredembodiment, it is five bits and it is received by antenna 22 oftransponder 20 and input to receiver 44.

A temperature module 30 is coupled to a thermistor 32. Thermistor 32changes resistance as a function of temperature and outputs a frequencysignal which changes with resistance. Temperature module 30 continuouslycounts the output of thermistor 32 and outputs the current count as aTEMP DATA signal to data module 40.

In step 306 receiver 44 receives the temperature command and outputsXMIT COMPLETE signal to address module 38 upon completion of thetemperature command. The XMIT COMPLETE signal is also output to clockgenerator 36 and program control 46. Clock generator 36 outputs a LATCHTEMP signal to data module 40 on a periodic basis. At each occurrence ofthe LATCH TEMP signal, data module 40 outputs the current count of theTEMP DATA signal as a DATA OUT signal to transmitter 42. Transmitter 42then outputs the latched count as the XMIT OUT signal to modulator 34which modulates the signal and outputs the temperature count fromantenna 22 to interrogator 10.

Because the frequency monitored by temperature module 30 varies withtemperature, the count rate will vary with temperature. Clock generator36, by outputting a consistent periodic LATCH TEMP signal at apredetermined interval, is utilized to standardize the sampling. This isdone to reflect the changes in count as a function in temperature andnot of time. In effect, each temperature sampling is the differencebetween successive latched counts.

Reference is made to FIG. 9B in which the steps 306 for readingtransponder temperature data are provided in greater detail. CPU 12 ofinterrogator 10 has as part of its software a read tries counter. Instep 308, the read tries counter is set to zero. In step 310, thetemperature data is read as described above i.e. reading a plurality oflatched samples. Interrogator 10 outputs a read command signal whichresults in interrogator 10 receiving a predetermined number of latchedcounts from temperature module 30. The read tries counter is incrementedin a step 312. It is determined whether or not the counter for number ofread tries exceeds a predetermined maximum in a step 314. If the numberof tries has been exceeded, then this is an indicator that thetemperature readings are inaccurate, and the temperature reading hasbeen unsuccessful (step 324) because it is requiring too many tries toobtain an accurate reading and the process is begun again in a step 300in which transponder data is read.

If the counter for the number of read tries has not exceeded themaximum, then the read has been successful and the temperature datasamples are totaled in step 316. In step 318, as an integrity check, itis determined whether the difference between the count for the smallestdata sample and the count for the largest data sample is within apredetermined range. If it falls outside of the range, then thevariation is too great and the process is begun again at a step 310.

If the value is within the range, the total data sample temperature fromstep 316 is then divided by the amount of time required to generate allof the data in a step 320. This is the frequency output by thethermistor. Knowing the relationship between frequency and temperaturefor the given thermistor, the temperature is calculated in a step 322.In a step 324, it is determined whether the transponder read wassuccessful. If not, the process is begun again at step 300. If the readwas successful, then for verification a second read is taken in a step326 by repeating steps 308-322. In a step 328 it is determined whetherthe second read was successful. If not, the process is restarted at step300. If successful then the two counts are compared in a step 330. Ifthey are equal, this temperature is displayed by interrogator 10. Ifthey are not equal then the process is restarted at step 300.

Integrity Check

In one embodiment of the invention, the interrogator performs anintegrity check of the data being read from transponder 20. Becausetransponder 20 utilizes the interrogator signal from interrogator 10 asa master clock, interrogator 10 knows the length of time between bits ofdata transmitted to interrogator 10 by transponder 20. CPU 12 ofinterrogator 10 includes an accumulator. In a step 400, the accumulatoris set to zero. In a step 402, the first transponder bit is received. Ina step 404, the next transponder data bit is received. In a step 406utilizing an on-board clock, interrogator 10 calculates the actual timeelapsed between the last successive two data bits. In a step 408, thecalculated time in a step 406 is subtracted from the average timeexpected between two bits. This number is an error number. In a step410, the error number is added to the accumulator. In a step 412, it isdetermined whether the accumulator value is greater than an errordetection constant. If the value is greater than an error detectionconstant, than this means the data is out of phase, and in a step 413interrogator 10 stops receiving data from the transponder 20 and startsthe read process over. If in step 412 the detection constant is stillwithin acceptable tolerances, it is determined in a step 414 whetherthere are any more incoming transponder data bits. If there are moreincoming bits, then the process is repeated at a step 404. If there areno more bits, then the received data is valid and the process is ended.

By utilizing the method, it is no longer required to wait until the veryend of the read cycle to determine whether or not a bad read hasoccurred. Time is saved by arriving at an accurate read more quicklyproviding a benefit to the user.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in carrying out the above method inthe construction(s) set forth without departing from the spirit andscope of the invention, it is intended that all matter contained in theabove description and shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

1. A method for determining temperature from a transponder utilizing athermistor and a running counter comprising the steps of: providing arunning count which varies as a function of temperature; latching thecount at predetermined time intervals; determining the differencebetween the values of successive latched counts; aggregating thedifferences; determining the total elapsed time between a first latchedcount and a last latched count; dividing the aggregate by the total timeto obtain a frequency; and converting the frequency to a temperaturebased upon the temperature frequency characteristics of the thermistor.2. The method of claim 1, comprising the step of determining thedifference between the smallest difference obtained and the largestdifference obtained and determining whether or not the second differencefalls within a range; beginning the process over if the difference doesnot fall within the range.
 3. The method of claim 2, further comprisingrepeating the steps to obtain a second temperature value; comparing afirst temperature value to the second temperature value; and outputtingthe temperature as a temperature value if the first temperature value isequal to the second temperature value.